How would you reacted?

So my son is amazing when he plays with others. Barely if ever pushes or steals toys and shares really well. Today we were at a play group and my son initially started going for Thomas the Train but another little girl got it first. My son made eye contact with him and I reassured him that it's okay, you can play with it later and to find another toy. As he was turning around to find another toy the other child literally wacked his head with the toy. It was super hard and my guy just bursted out and cried - from pain and absolute surprise because he had no happened. Now I get it, kids will be kids but I didn't agree with the mom's reaction. Personally if my child did this, I would pull my child aside and tell them why this is not okay and then bring them to the other child and say sorry and give the toy. there has to be some reprecussion right? all she did was sit where she was - didn't even get up from her seat - and say sorry herself. like ummm parent your child! i dont think i am off on this but thought to check in on your thoughts?